The invention is related generally to the remote viewing of well bores and other limited access areas, and more particularly to an apparatus having a camera for remotely viewing the condition of such limited access areas.
There has long been a need in the field of well boring to visually examine the bore hole to examine geological formations or for other reasons. Where those well bores have casings and fittings, there is a continuing need to inspect the casings and fittings for corrosion and other conditions. By means of visual inspection, the locations of leaks and points of infiltration can be more easily identified.
One existing method of accomplishing this is to insert an instrument probe containing a camera such as a dosed circuit television camera, in the bore hole and move it through the area to be inspected. Typically, a compact, rugged instrument containing the camera and a light source is provided as an instrument probe. A cable is attached between the instrument probe and the surface station to communicate camera signals to the surface from the instrument probe. In one technique, the communication link comprises optical fibers. Where the bore is vertical, gravity can be used to pull the instrument probe through the bore hole. The support cable contains strength members which preserve the integrity of the cable as it and the instrument probe are being pulled from the bore hole.
Optical fibers offer certain advantages in communication systems. They are relatively immune to electromagnetic interference, they have relatively low cable weight, they have a large bandwidth, high frequency video signals can be transmitted over long lengths of cable with minimum attenuation and they have lower cost. Thus they are desirable in a remote logging instrument probe such as that used to view bore holes. However, optical fibers are sensitive to point stresses and bending. The fiber may impart significant attenuation to its conducted signal when bent. The cable system of a well logging instrument is repeatably pulled around at least one sheave and wound on and off a winch drum as it is lowered into and lifted out of bore holes. The cable must withstand repeated bending and tensions of thousands of pounds. Stretching the cable can stretch the optical fibers thereby increasing their stress and aggravating their attenuation. High pressures and high temperatures in the well holes may assist moisture in invading the cable and the optical fibers. Moisture invading the optical fiber through micro-cracks can increase its attenuation and reduce its strength. Thus, the cable connecting the instrument probe with the remote controller must protect the optical fibers as well as be strong enough to withstand repeated bending about sheaves and a winch drum, withstand stretching forces and the high temperatures and pressures in the bore hole.
A logging instrument probe for well holes must be rugged to withstand the sometimes harsh conditions encountered in typical operation. For example, hydrostatic well pressures in excess of 4.2.times.10.sup.6 kilograms per square meter (6,000 pounds per square inch) and ambient wall temperatures of up to and above 190.degree. C. (375.degree. F.) are not uncommon. The point where the support cable enters the instrument probe must have effective seals to deflect such high pressure/temperature fluids from entering. The main purpose of such seals is to protect the camera, the optical fibers and the electrical connections from the fluids present in the bore hole. Such seals have been difficult to manufacture on a repeatable basis and make the instrument probe very expensive as well as unreliable. Thus, it would be desirable to provide an effective seal arrangement which can be manufactured on a repeatable basis and which uses standard parts readily available thereby lowering the cost of the seal.
Another common condition in bore holes is turbidity in the form of gases, mud, oil, and other fluids under high pressure. In prior techniques, high intensity lighting such as that provided by quartz lamps or halogen lamps, is provided to give bright light in the visible range for use with conventional television cameras. Depending upon the amount of turbidity, higher intensity light from the lamps may be required to provide clear images.
In order to provide power for such lamps and for the camera and other equipment, well bore inspection instruments carry a self-contained power supply, typically battery packs. In addition to adding weight and bulk to the instrument probe, these battery packs have a limited life which is directly dependent upon the intensity of the lights. As an example, many battery packs of the size which can fit in a bore hole logging instrument probe can provide power for only 3 to 31/2 hours when used with halogen lamps. Upon dissipation of the stored energy, the battery packs must be removed and replaced with charged batteries or a charging process must occur which may take many hours. This usually requires that the instrument probe be removed from the well hole, dis-assembled and re-assembled. This can be a time consuming process which subjects the support cable of the instrument probe to the added stresses of being pulled over the sheave and wound on the drum an additional time.
To the inventor's knowledge, remotely locating a power source has up until this time not been practical in an application where a small diameter optical fiber is employed in the support cable having the extremely long lengths required for deep well holes. The power source has been included in the instrument probe itself. This co-location of power source with instrument probe was caused by the long lengths of cable required for use in deep well bores. In prior cables, the steel strength members of the cable were used as part of the electrically conductive path. Typically, the strength members are made of steel which has a relatively high specific resistance, and therefore a low resistive loop circuit was not available to carry the required current at an acceptable working voltage. The diameter of the strength members was increased to result in less resistance; however, even with this technique, the loop resistance was relatively high and the increased size of the strength members resulted in a large cable with the associated disadvantages of high weight and bulk. Additionally, such strength members were used to form the outer surface of the cable, thus making it rough and more difficult to handle.
Hence, it would be desirable to provide an improved power arrangement so that the power source for the well logging instrument probe could be remotely located from the probe, such as at the surface, yet impracticably large voltages would not be required in order to get the required power over the typically long distances between the surface and the probe. Additionally, it would be desirable to provide a smaller support cable and a support cable having a smooth outer surface to facilitate handling, yet one having the required strength. Additionally, those concerned with instrument probes for use in viewing bore holes and casing have recognized the need for an improved sealing system to keep fluids from entering the probe which can be manufactured on repeatable and economical bases. The invention fulfills those needs.